Insertion tool for a cochlear implant electrode array

ABSTRACT

A cochlear implant electrode assembly device ( 10 ) comprising an elongate electrode carrier member ( 11 ), and a shape element ( 15 ) formed of a memory material, such as Nitinol. The elongate member (11) is made of a resiliently flexible first material and has a length and a plurality of electrodes ( 12 ) mounted thereon adapted to apply a preselected tissue stimulation. The elongate member ( 11 ) has a pre-formed curved orientation that at least substantially matches an inside surface of a cochlea, an implantable orientation different to said pre-formed orientation that allows said member to be inserted into an implantee&#39;s cochlea, and an at least one intermediate orientation between said implantable orientation and said pre-formed orientation. The shape element ( 15 ) is removably positioned within the elongate member ( 11 ) and extends along at least a portion of the length thereof. The shape element ( 15 ) has a first shape selected for biasing the elongate member ( 11 ) into the implantable orientation when the shape element is at a first temperature, and at least a second shape that allows the elongate member ( 11 ) to adopt said at least one intermediate orientation when the shape element ( 15 ) is exposed to a temperature of the cochlea ( 30 ) being different than the first temperature.

FIELD OF THE INVENTION

[0001] The present invention relates to an implantable device and, inparticular, to all implantable cochlear electrode assembly.

BACKGROUND OF THE INVENTION

[0002] Hearing loss, which may be due to many different causes, isgenerally of two types, conductive and sensorineural. Of these types,conductive hearing loss occurs where the normal mechanical pathways forsound to reach the hair cells in the cochlea are impeded, for example,by damage to the ossicles. Conductive hearing loss may often be helpedby use of conventional hearing aid systems, which amplify sound so thatacoustic information does reach the cochlea and the hair cells.

[0003] In many people who are profoundly deaf, however, the reason fordeafness is sensorineural hearing loss. This type of hearing loss is dueto the absence of, or destruction of, the hair cells in the cochleawhich transduce acoustic signals into nerve impulses. These people arethus unable to derive suitable benefit from conventional hearing aidsystems, because there is damage to or absence of the mechanism fornerve impulses to be generated from sound in the normal manner.

[0004] It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.U.S. Pat. No. 4,532,930, the contents of which are incorporated hereinby reference, provides a description of one type of traditional cochlearimplant system.

[0005] Cochlear implant systems have typically consisted of two keycomponents, namely all external component commonly referred to as aprocessor unit, and an implanted internal component commonly referred toas a stimulator/receiver unit. Traditionally, both of these componentshave cooperated together to provide the sound sensation to an implantee.

[0006] The external component has traditionally consisted of amicrophone for detecting sounds, such as speech and environmentalsounds, a speech processor that converts the detected sounds andparticularly speech into a coded signal, a power source such as abattery, and an external antenna transmitter coil.

[0007] The coded signal output by the speech processor is transmittedtranscutaneously to the implanted stimulator/receiver unit situatedwithin a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs through use of an inductive couplingprovided between the external antenna transmitter coil which ispositioned to communicate with an implanted antenna receiver coilprovided with the stimulator/receiver unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedstimulator/receiver unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

[0008] The implanted stimulator/receiver unit typically included theantenna receiver coil that receives the coded signal and power from theexternal processor component, and a stimulator that processes the codedsignal and outputs a stimulation signal to an intracochlea electrodeassembly which applies the electrical stimulation directly to theauditory nerve producing a hearing sensation corresponding to theoriginal detected sound.

[0009] The external componentry of the cochlear implant has beentraditionally carried on the body of the implantee, such as in a pocketof the implantee's clothing, a belt pouch or in a harness, while themicrophone has been mounted on a clip mounted behind the ear or on aclothing lapel of the implantee.

[0010] More recently, due in the main to improvements in technology, thephysical dimensions of the speech processor have been able to be reducedallowing for the external componentry to be housed in a small unitcapable of being worn behind the ear of the implantee. This unit hasallowed the microphone, power unit and the speech processor to be housedin a single unit capable of being discretely worn behind the ear, withthe external transmitter coil still positioned on the side of the user'shead to allow for the transmission of the coded sound signal from thespeech processor and power to the implanted stimulator unit.

[0011] Together with improvements in available technology much researchhas been undertaken in the area of understanding the way sound isnaturally processed by the human auditory system. With such an increasedunderstanding of how the cochlea naturally processes sounds of varyingfrequency and magnitude, there is a need to provide an improved cochlearimplant system that delivers electrical stimulation to the auditorynerve in a way that takes into account the natural characteristics ofthe cochlea.

[0012] It is known in the art that the cochlea is tonotopically mapped.In other words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea is exploited by providing the electrode assemblywith all array of electrodes, each electrode being arranged andconstructed to deliver a cochlea stimulating signal within a preselectedfrequency range to the appropriate cochlea region. The electricalcurrents and electric fields from each electrode stimulate the ciliadisposed on the modiola of the cochlea. Several electrodes may be activesimultaneously.

[0013] It has been found that in order for these electrodes to beeffective, the magnitude of the currents flowing from these electrodesand the intensity of the corresponding electric fields, are a functionof the distance between the electrodes and the modiola. If this distanceis relatively great, the threshold current magnitude must be larger thanif the distance is relatively small. Moreover, the current from eachelectrode may flow in all directions, and the electrical fieldscorresponding to adjacent electrodes may overlap, thereby causingcross-electrode interference. In order to reduce the thresholdstimulation amplitude and to eliminate cross-electrode interference, itis advisable to keep the distance between the electrode array and themodiola as small as possible. This is best accomplished by providing theelectrode array in the shape which generally follows the shape of themodiola. Also, this way the delivery of the electrical stimulation tothe auditory nerve is most effective as the electrode contacts are asclose to the auditory nerves that are particularly responsive toselected pitches of sound waves.

[0014] In order to achieve this electrode array position close to theinside wall of the cochlea, the electrode needs to be designed in such away that it assumes this position upon or immediately followinginsertion into the cochlea. This is a challenge as the array needs to beshaped such that it assumes a curved shape to conform with the shape ofthe modiola and must also be shaped such that the insertion processcauses minimal trauma to the sensitive structures of the cochlea. Inthis sense it has been found to be desirable for the electrode array begenerally straight during the insertion procedure.

[0015] Several procedures have been adopted to provide an electrodeassembly that is relatively straightforward to insert while adopting acurved configuration following insertion in the cochlea. In one case, aplatinum wire stylet is used to hold a pre-curved electrode array in agenerally straight configuration up until insertion. Followinginsertion, the platinum stylet is withdrawn allowing the array to returnto its pre-curved configuration.

[0016] In another development, a bimetallic filament (such asnickel/titanium) or a filament made of a nickel/titanium alloy ispositioned in the electrode assembly and used to again hold a pre-curvedelectrode array in a generally straight configuration while the array isat about room temperature. On insertion into the body and exposure tobody temperature, the filament bends into a pre-selected curvedconfiguration.

[0017] In a still further arrangement, a longitudinal element that isarranged on one side of the array and constructed to change itsdimension on insertion can be utilised. For example, the longitudinalelement could include a hydrogel such as polyacrylic acid (PAA) whichexpands after insertion by absorbing water from the cochlear fluid.

[0018] In developing such electrode array designs, it is of greatimportance that the design be constructed to minimise potential damageto sensitive structures in the cochlear on insertion and placement. Eachof the above constructions suffer from a number of disadvantages in thisregard.

[0019] Still further, it has been proposed to straighten pre-curvedelectrode arrays using inserted longitudinal elements or surroundingsheaths formed from bioresorbable materials that dissolve or soften onimplantation. A disadvantage with use of such bioresorbable materials isthat, due to the generally wet nature of the surgical environment, thepolymer can dissolve or soften before the electrode array isappropriately positioned.

[0020] U.S. Pat. No. 6,119,044 provides a description of anotherarrangement adapted to ensure electrode contacts of an implantable arrayare against the modiolar wall of the cochlea following implantation. Inthis arrangement, a positioning wire made from memory wire is positionedin a longitudinal channel of the array. On insertion into the cochleaand exposure to body temperature, the positioning wire is adapted toadopt a curved spiral shape which causes the electrode contacts to beforced against the modiolar wall.

[0021] In this arrangement, the positioning wire serves to maintain theelectrode array in its spiral configuration following implantation andprovides a permanent bending force to the electrode array to ensure thatthe spiral configuration is adopted. A disadvantage of this arrangementis that should for any reason the array require replacement or removal,such an arrangement would be difficult to remove without causing damageto the delicate structures of the cochlea.

[0022] The present invention is directed to an electrode assemblyadapted to overcome some of the difficulties of prior art electrodeassemblies.

[0023] Any discussion of documents, acts, materials, devices, articlesor the like which has been included in the present specification issolely for the purpose of providing a context for the present invention.It is not to be taken as an admission that any or all of these mattersform part of the prior art base or were common general knowledge in thefield relevant to the present invention as it existed in Australiabefore the priority date of each claim of this application.

SUMMARY OF THE INVENTION

[0024] Throughout this specification the word “comprise”, or variationssuch as “comprises” or “comprising”, will be understood to imply theinclusion of a stated element, integer or step, or group of elements,integers or steps, but not the exclusion of any other element, integeror step, or group of elements, integers or steps.

[0025] According to a first aspect, the present invention is animplantable tissue-stimulating device comprising:

[0026] an elongate member made of a resiliently flexible first materialand having a length and a plurality of electrodes mounted thereonadapted to apply a preselected tissue stimulation, the elongate memberhaving a pre-formed orientation, an implantable orientation different tosaid pre-formed orientation that allows said member to be inserted intoan implantee's body, and an at least one intermediate orientationbetween said implantable and said pre-formed orientation; and

[0027] a shape element removably positioned within the elongate memberand extending along at least a portion of the length thereof, saidelement having:

[0028] a first shape selected for biasing said elongate member into saidimplantable orientation when the shape element is at a firsttemperature; and

[0029] at least a second shape that allows the elongate member to adoptsaid at least one intermediate orientation when the shape element isexposed to a pre-determined temperature different than said firsttemperature.

[0030] In a preferred embodiment of this aspect, the pre-formedorientation of the elongate member is curved. More preferably, theelongate member adopts a spiral curvature when in the pre-formedorientation.

[0031] According to a second aspect, the present invention is a cochlearimplant electrode assembly device comprising:

[0032] an elongate electrode carrier member made of a resilientlyflexible first material and having a length and a plurality ofelectrodes mounted thereon adapted to apply a preselected tissuestimulation, the elongate member having a pre-formed curved orientationthat at least substantially matches an inside surface of a cochlea, animplantable orientation different to said pre-formed orientation thatallows said member to be inserted into an implantee's cochlea, and an atleast one intermediate orientation between said implantable orientationand said pre-formed orientation; and

[0033] a shape element removably positioned within the elongate memberand extending along at least a portion of the length thereof, saidelement having:

[0034] a first shape selected for biasing said elongate member into saidimplantable orientation when the shape element is at a firsttemperature; and

[0035] at least a second shape that allows the elongate member to adoptsaid at least one intermediate orientation when the shape element isexposed to a temperature of the cochlea being different than said firsttemperature.

[0036] In this invention, the shape element biases the elongate memberin the implantable orientation and serves to prevent the elongate memberadopting its preferred pre-formed orientation, such as the pre-formedcurved orientation defined in the second aspect. This is in contrast tothe situation described in U.S. Pat. No. 6,119,044 where the positioningwire is adapted to control the orientation of the flexible carrier inall orientations.

[0037] In a preferred embodiment of each aspect, the shape element isformed from a shape memory material. The shape memory material ispreferably relatively stiffer than the first material. In oneembodiment, the shape memory material can be a nickel-titanium alloy orNitinol. In another embodiment, the shape memory material can be aplastics material or made from another non-metal shape memory material.In a preferred embodiment, the shape memory material of the shapeelement is used to hold the elongate member of the electrode array in agenerally straight orientation while the array is at about roomtemperature or at least a temperature different to body temperature(about 37° C.). On insertion into the body and exposure to bodytemperature, the shape element adopts the second shape. In oneembodiment, the second shape allows the elongate member to adopt acurved orientation in which the tip of the elongate member has adoptedat least a degree of curvature.

[0038] In a preferred embodiment, the shape element is removable fromthe elongate member once the elongate member has adopted its said atleast one intermediate orientation. On removal of the shape element, theelongate member preferably adopts its pre-formed orientation.

[0039] The elongate member is preferably preformed from a plasticsmaterial with memory. The elongate member preferably has a first endthat is firstly inserted into the implantee.

[0040] In a preferred embodiment, the implantable orientation ispreferably substantially straight. More preferably, the implantableorientation is straight.

[0041] In a preferred embodiment, the elongate member is formed from asuitable biocompatible material. In one embodiment, the biocompatiblematerial can be a silicone, such as a flexible siliconeelastomer-Silastic. Silastic MDX 4-4210 is an example of one suitablesilicone for use in the formation of the elongate member. In anotherembodiment, the elongate member call be formed from a polyurethane orsimilar material.

[0042] In a further embodiment, the elongate member can have aresiliently flexible tip member extending forwardly from the first endof the body. The tip member preferably has a distal end and a proximalend. The tip member call have a stiffness that is relatively less stiffthan said stiffening element. The tip member can further be formed of amaterial that is substantially the same or the same stiffness as thebody of the elongate member. In another embodiment, the tip member canbe formed of a material that is relatively less stiff than at least aportion of the elongate member. In a further embodiment, the tip membercall be formed of a material that undergoes a change in stiffness,preferably a decrease in stiffness, on insertion into the body, such asthe cochlea.

[0043] In a further embodiment, the stiffness of the tip member can varyalong at least a portion of its length from its distal end to itsproximal end. In one embodiment, the stiffness of the tip member canvary over the entire length of the tip member or only a portion thereof.The stiffness can increase from the distal end to the proximal end. Inone embodiment, the stiffness of the tip member over said portion or itslength can increase gradually from its distal end towards to theproximal end. The increase in stiffness can be substantially smooth orincrease in a stepwise fashion.

[0044] In a further embodiment, the tip member can be formed of the samematerial as the body of the elongate member. In another embodiment, thetip member can be formed of a different material to that of the body ofthe elongate member. The tip member can be comprised of an innerrelatively stiff core of material having a tapered end, with at leastthe tapered end being overlaid by a relatively flexible material thatextends beyond the tapered end of the core material so that the tipmember undergoes a gradual decrease in flexibility in the region of thetapered end of the core moving away from the distal end.

[0045] The tip member can be formed separately to the body of theelongate member and mounted thereto. For example, the tip member call beadhered to the first end of the body of the elongate member. In anotherembodiment, the tip member can be integrally formed with the body of theelongate member. The tip member can be formed from a silicone material.In another embodiment, the tip member can be formed of an elastomericmaterial, such as polyurethane.

[0046] In another embodiment, the tip member can have a plurality ofmetallic particles dispersed therethrough. The metallic particles can besubstantially evenly dispersed through the tip member. Alternatively,the metallic particles can be non-evenly dispersed throughout the tipmember. In one embodiment, the metallic particles can increase indensity away from the distal end towards the proximal end of the tipmember. By varying the density of the metallic particles, it is possibleto vary the relative stiffness of the tip member.

[0047] The metallic particles preferably comprise a biocompatiblematerial, such as platinum. The particles can be substantially sphericalor spherical. It will be appreciated that the particles can have othersuitable shapes. In one embodiment, the particles can have a diameterbetween about 50 μm and 100 μm.

[0048] In addition to, or instead of, being used to potentially modifythe physical characteristics of the tip member, the provision of themetallic particles also result in the tip member being detectable byfluoroscopy and X-ray techniques. This provides another means for thesurgeon to monitor the placement and position of the tip member duringor after insertion of the electrode array in the body, such as in thecochlea.

[0049] When the elongate member is in the first configuration, the tipmember is preferably substantially straight and, more preferably,straight.

[0050] In a further embodiment, the tip member can be coated with alubricious material. The lubricious material can be a bioresorbable ornon-bioresorbable material.

[0051] The tip member can be formed from, or incorporate as a portionthereof, a bioresorbable material. The presence of the bioresorbablematerial preferably results in the flexibility of the tip memberincreasing on insertion of the tip member into the body, such as thecochlea. The bioresorbable material in the tip member can be selectedfrom the group consisting of polyacrylic acid (PAA), polyvinyl alcohol(PVA), polylactic acid (PLA) and polyglycolic acid (PGA).

[0052] In another embodiment, the tip member can be formed from, orincorporate as a portion thereof, a polymeric coating which becomessofter, and so increases in resilient flexibility, in the presence ofmoisture or body heat. The tip member preferably has a length from itsdistal end to its proximal end in the range of about 0.3 to 4 mm, morepreferably about 1.0 to 3.0 mm. The diameter of the tip member can besubstantially constant for a majority of its length or can vary indiameter. The tip member can be substantially cylindrical, cylindrical,or non-cylindrical for a majority of its length. At the distal end, thediameter preferably gradually decreases to form a rounded end. Themaximum diameter of the tip member is preferably about 0.55 mm.

[0053] In one embodiment, the tip member can be solid. In anotherembodiment, the tip member can have an external wall defining a cavity.In one embodiment, the cavity can have a diameter greater than that ofthe receiving portion of the body of the elongate member. In a furtherembodiment, the cavity can extend from the proximal end towards thedistal end of the tip member. The cavity can decrease in diameter awayfrom the proximal end. The cavity can be in communication with a distalend of the receiving portion of the body of the elongate member. In afurther embodiment, the stiffening means can extend into the cavity whenpositioned within the device or assembly according to the respectiveaspects of the present invention. In a preferred embodiment, the tipmember can move relative to the stiffening means when it extends intothe cavity of the tip member.

[0054] In general, the tip could be made of a combination of materialsarranged in a variety of geometries depending on the specific designgoal. The outside shape and size of the tip can also be made in avariety of forms depending on the design goal.

[0055] In one embodiment, the shape element can be removably positionedin a lumen extending through the elongate member for at least a portionof its length. In one embodiment, the lumen extends through the elongatemember for a substantial portion of its length. In a further embodiment,the lumen extends from an opening distal the first end to or adjacentthe first end. The shape element preferably extends the entire length ofthe lumen in the elongate member.

[0056] The lumen can be cylindrical or have another cross-sectionalshape. The shape element can extend out of the opening allowing theelement to be manipulated and removed from the lumen during insertion ofthe device.

[0057] The shape element can also be cylindrical, such as a wire, orcould have another cross-sectional shape, such as oval, rectangular,triangular and others. The shape element could also be tapered along itslength to achieve graduation in stiffness and strength, or have othernon-uniform cross-sectional shapes along its length to achieveparticular desirable bending characteristics.

[0058] In a further embodiment, the elongate member can have an outerlayer. The outer layer can act as a stiffening sheath for the elongatemember. The stiffening sheath can be formed of a bioresorbable materialwhich dissolves or softens on exposure to a fluid. The stiffening sheathcan dissolve or soften on exposure to a saline solution or a body fluidof the implantee, such as cochlear fluid.

[0059] In a further embodiment, the bioresorbable material of thestiffening sheath is selected from the group comprising polyacrylic acid(PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolicacid (PGA). It is also envisaged that other suitable materials could beused.

[0060] The device can include all additional layer surrounding thestiffening sheath. The additional layer can have a first rate of fluidingress therethrough and have at least one fluid ingress means formedtherein, the rate of fluid ingress through the fluid ingress means beinggreater than the first rate of fluid ingress through the additionallayer.

[0061] The fluid ingress means can comprise one or more openings in theadditional layer. The openings can be closable. The openings cancomprise slits in the additional layer. The slits can be formed to allowsubstantially the same or the same rate of ingress of fluid through theadditional layer. In another embodiment, at least one slit can allow adifferent rate of progress of fluid through the additional layercompared to the other slits.

[0062] The purpose of allowing the elongate member to adopt theintermediate orientation, following insertion into the cochlea, is toenable the elongate member to be inserted into the cochlea in a waywhich minimises trauma to the walls of the cochlea. The preferred shapeof this intermediate orientation is for the elongate member to assume ashape that is more curved than the straight orientation present uponinsertion. By having the previously straight array adopt a more curvedshape, the elongate member is guided to adopt a mid-scala trajectory asit is inserted into the cochlea. This ensures that as the elongatemember is carefully inserted deeper into the spiral shaped cochlea, theintermediate curved orientation assists in ensuring that the elongatemember can be inserted deep into the cochlea without causing excessivetrauma to the walls of the cochlea.

[0063] On subsequent removal of the shape element, the elongate memberis free to adopt the fully curved pre-formed orientation desired of animplant for final position in the cochlea.

[0064] The present invention provides a surgeon with a means to at leastpartially control the rate of curvature formation in a cochlearelectrode assembly during insertion into the cochlea. Such increasedcontrol is envisaged to reduce the potential for trauma to the cochleacaused by electrode assembly insertion. The present invention alsoprovides a means of assisting the insertion process of the electrodeassembly into the cochlea by allowing the electrode assembly to alterits orientation during the insertion process to allow for more desirablecochlea penetration and/or electrode positioning.

[0065] In a further embodiment, at least a portion of an outer surfaceof the elongate member can have a coating of a lubricious material. Inone embodiment, a substantial portion or the entire outer surface of theelongate member can have a coating of the lubricious material.

[0066] In this embodiment, the lubricious material can be selected fromthe group comprising polyacrylic acid (PAA), polyvinyl alcohol (PVA),polylactic acid (PLA) and polyglycolic acid (PGA). It is envisaged thatother similar materials could also be used.

[0067] In a further aspect, the present invention comprises a method ofimplanting a tissue-stimulating device or cochlear electrode assemblydevice as defined herein in a body of an implantee.

[0068] In this aspect, the method can comprise a step of accessing theimplantation site and then a step of inserting the device. Prior toinsertion, the device is preferably substantially straight or straight.On insertion, the elongate member can adopt an intermediate orientation(as defined herein). Following full insertion and after removal of theshape element, the device has preferably adopted its pre-formedorientation.

[0069] Once implanted, the electrodes can receive stimulation signalsfrom a stimulator means. The stimulator means is preferably electricallyconnected to the elongate member by way of an electrical lead. The leadcan include the one or more wires extending from each electrode of thearray mounted on the elongate member.

[0070] In one embodiment, the lead can extend from the elongate memberto the stimulator means or at least the housing thereof. In oneembodiment, the lead is continuous with no electrical connectors, atleast external the housing of the stimulator means, required to connectthe wires extending from the electrodes to the stimulator means. Oneadvantage of this arrangement is that there is no requirement for thesurgeon implanting the device to make the necessary electricalconnection between the wires extending from the electrodes and thestimulator means.

[0071] The stimulator means is preferably positioned within a housingthat is implantable within the implantee. The housing for the stimulatormeans is preferably implantable within a recess in the bone behind theear posterior to the mastoid.

[0072] When implanted, the housing preferably contains, in addition tothe stimulator means, a receiver means. The receiver means is preferablyadapted to receive signals from a controller means. The controller meansis, in use, preferably mounted external to the body of the implanteesuch that the signals are transmitted transcutaneously through the skinof the implantee.

[0073] Signals can preferably travel from the controller means to thereceiver means and vice versa. The receiver means can include a receivercoil adapted to receive radio frequency (RF) signals from acorresponding transmitter coil worn externally of the body. The radiofrequency signals can comprise frequency modulated (FM) signals. Whiledescribed as a receiver coil, the receiver coil can preferably transmitsignals to the transmitter coil which receives the signals.

[0074] The transmitter coil is preferably held in position adjacent theimplanted location of the receiver coil by way of respective attractivemagnets mounted centrally in, or at some other position relative to, thecoils.

[0075] The external controller can comprise a speech processor adaptedto receive signals output by a microphone. During use, the microphone ispreferably worn on the pinna of the implantee, however, other suitablelocations can be envisaged, such as a lapel of the implantee's clothing.The speech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for cochlear implant systems. The encodedsequence is transferred to the implanted stimulator/receiver means usingthe transmitter and receiver coils. The implanted stimulator/receivermeans demodulates the FM signals and allocates the electrical pulses tothe appropriate attached electrode by an algorithm which is consistentwith the chosen speech coding strategy.

[0076] The external controller further comprises a power supply. Thepower supply can comprise one or more rechargeable batteries. Thetransmitter and receiver coils are used to provide power viatranscutaneous induction to the implanted stimulator/receiver means andthe electrode array.

[0077] While the implant system can rely on external componentry, inanother embodiment, the controller means, including the microphone,speech processor and power supply can also be implantable. In thisembodiment, the controller means can be contained within a hermeticallysealed housing or the housing used for the stimulator means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] By way of example only, a preferred embodiment of the inventionis now described with reference to the accompanying drawings, in which:

[0079]FIG. 1 is a simplified cross-sectional view of one embodiment ofan electrode assembly according to the present invention depicted in itsimplantable orientation;

[0080]FIG. 2 is a simplified side elevational view of the electrodeassembly of FIG. 1 depicted in an intermediate orientation;

[0081]FIG. 3 is a simplified part-sectional, part side elevational viewof the electrode assembly depicted in its pre-formed orientationfollowing insertion in the cochlea; and

[0082]FIG. 4 is a simplified cross-sectional view of another embodimentof an electrode assembly according to the present invention; and

[0083]FIGS. 5a-5 d depict alternative tip structures for the electrodeassembly depicted in FIG. 4.

PREFERRED MODE OF CARRYING OUT THE INVENTION

[0084] One embodiment of a cochlear implant electrode assembly accordingto the present invention is depicted generally as 10 in the drawings.

[0085] The depicted electrode assembly 10 has an electrical leadextending back to a stimulator/receiver housing. In considering thisinvention, it is to be understood that each electrode 12 may have one ormore wires (not depicted) electrically connected thereto and extendingfrom each respective electrode 12 back through the lead to thestimulator/receiver.

[0086] The assembly 10 comprises an elongate electrode carrier member 11having a plurality of electrodes 12 mounted thereon. For the purposes ofclarity, the electrodes 12 depicted in FIG. 1 are not necessarily shownto scale. A larger number of electrodes than that depicted in FIG. 1 canalso be envisaged. The electrodes 12 are not depicted in FIGS. 2 and 3for reasons of clarity.

[0087] The depicted elongate member 11 is preformed from a resilientlyflexible silicone with memory and is preformed to a curved orientationsuitable for insertion in the scale tympani 31 of a patient's cochlea30. The elongate member 11 has a first end 13 that is firstly insertedinto the cochlea 30 upon insertion of the assembly 10.

[0088] As depicted in FIG. 4, the elongate member 11 can have a tipmember 29, having a different construction to that depicted in FIG. 1,which is integrally formed with its first end 13. The tip 29 is formedfrom the same silicone used to fabricate the elongate member 11 and, inthe depicted embodiment, the material of tip member 29 has a resilientflexibility equal to that of the material used for the carrier member11.

[0089] Possible alternative constructions for the tip member 29 areprovided in FIGS. 5a-5 d. As depicted in FIG. 5a, the tip member 70 canbe solid and formed of an inner core 71 of relatively stiff material 71and an outer layer 72 of relatively flexible material. The core 71 cantaper in diameter over region 73 towards the distal end 21. The taper 73causes the overall stiffness of the tip 70 to increase over the lengthof the taper 73 away from the distal end 21. The outer layer 72 can beformed of the same material as the remainder of the body of the elongatecarrier member 11 or can be a different material.

[0090] As depicted in FIG. 5b, the tip member 40 can comprise a solidmass integrally formed to the first end 13 of the elongate carrier 11.

[0091] Still further and as depicted in FIG. 5c, the tip member 50 cancomprise a solid mass 51 that is formed separately from the carriermember 11 and subsequently adhered thereto.

[0092] As depicted in FIG. 5d, the tip member 60 can comprise anelastomeric silicone material having a plurality of substantiallyspherical platinum particles 61 dispersed therethrough. The particles 61have a diameter between about 50 μm and 100 μm. It will be appreciatedthat the particles 61 depicted in FIG. 6d are not drawn to scale.

[0093] In FIG. 5d, the particles 61 are depicted as substantially evenlydispersed through the tip member 60. In another embodiment, theparticles could be non-evenly dispersed through the tip member. Forexample, the particles could increase in density away from the distalend 21 towards the proximal end of the tip member 60. By varying thedensity of the platinum particles 61, it is possible to vary therelative stiffness of the tip member 60.

[0094] In addition to, or instead of, being used to potentially modifythe physical characteristics of the tip member, the provision of themetallic particles 61 also result in the tip member 60 being detectableby fluoroscopy and X-ray techniques. This provides another means for thesurgeon to either monitor the placement and position of the tip member60 during or after insertion of the electrode array 10 in an implantee'scochlea.

[0095] Disposed within a lumen 14 is a nickel/titanium (Nitinol™) wire15. In the depicted embodiment, the wire 15 alone has a stiffness thatis sufficient to retain the silicone elongate member 11 in a straightorientation when the wire 15 is at room temperature (as shown in FIG.1).

[0096] Whilst a substantially cylindrical lumen is depicted, the lumen14 could indeed be any shape necessary to perform the function. The wire15 has a circular cross-section. Other shape elements having differentcross sections and forms can be envisaged.

[0097] As depicted in FIG. 2, the wire has a preferred direction of curlon exposure to body temperature within the cochlea. In one embodiment,the array 10 can have an indicia means that provides an indication to auser, such as a surgeon, of the of the preferred direction of curl ofthe array on implantation. This is important as the array 10 needs to beoriented in the cochlea such that the direction of curl results in thearray 10 being able to be moved into the scala tympani 31. The indiciameans can comprise a loop formed in the wire at or adjacent a distal endthereof. The loop as well as acting as an indicia means can act as ameans of engaging with and withdrawing the wire 15 from the lumen 14during or following implantation. In one embodiment, the loop can be inthe same plane as the preferred direction of curl of the wire 15. Theloop could extend away from the preferred direction of curl of the wire15.

[0098] In the embodiment shown in FIG. 1, overlaying the depictedelongate member 11 it is possible to provide a sheath 16 ofbioresorbable and lubricious material. The bioresorbable material of thedepicted stiffening sheath is PAA that is adapted to dissolve onexposure to cochlear fluids. Other suitable bioresorbable materials canbe envisaged and such materials need not necessarily dissolve onexposure to fluids. For example, the sheath can be made of a materialthat softens upon exposure to fluids but does not get absorbed.

[0099] While the elongate member 11 is manufactured with a preformedcurved orientation, the assembly 10 is typically delivered to a surgeonwith the Nitinol wire 15 in place. The wire 15, while at roomtemperature, holds the elongate member 11 in the straight orientationdepicted in FIG. 1.

[0100] Upon insertion into the scala tympani 31 of the cochlea 30, theexposure of the assembly 10 to body temperature (about 37° C.) resultsin the Nitinol wire 15 adopting a curved orientation. As the wire 15adopts the curved orientation, the elongate member 11 is free to alsoadopt the curved orientation as is depicted in FIG. 2.

[0101] As the elongate member 11 curls, the surgeon can continue tofurther insert the assembly 10 into the scala tympani 31. During thefurther insertion process, the surgeon can commence withdrawal of thewire 15 through opening 17 of the lumen 14 at end 18. Alternatively, thesurgeon may withdraw the wire 15 following complete insertion of theassembly into its final position, this decision being dependent of thesurgeon's preferences. Upon withdrawal of the wire 15, the elongatemember 11 is free to adopt its pre-formed spiral orientation (as isdepicted in FIG. 3), with the electrodes facing the modiola within thecochlea 30 so that they are positioned as close as possible to thespiral ganglia thereof.

[0102] The provision of the shape memory wire 15 provides the surgeonwith greater control of the implantation procedure for the cochlearimplant electrode assembly 10. The provision of greater controlminimises the potential for trauma to the sensitive tissues inside thecochlea and also enhances the likelihood of successful placement of theassembly 10 at the first attempt.

[0103] While the preferred embodiment of the invention has beendescribed in conjunction with a cochlear implant, it is to be understoodthat the present invention has wider application to other implantableelectrodes, such as electrodes used with pacemakers.

[0104] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. An implantable tissue-stimulating device comprising: a stimulatingmeans; an elongate member coupled to said stimulating means made of aresiliently flexible first material and having a length and a pluralityof electrodes mounted thereon adapted to apply a preselected tissuestimulation, the elongate member having a pre-formed orientation, animplantable orientation different to said pre-formed orientation thatallows said member to be inserted into an implantee's body, and an atleast one intermediate orientation between said implantable and saidpre-formed orientation; and a shape element removably positioned withinthe elongate member and extending along at least a portion of the lengththereof, said element having: a first shape selected for biasing saidelongate member into said implantable orientation when the shape elementis at a first temperature; and at least a second shape that allows theelongate member to adopt said at least one intermediate orientation whenthe shape element is exposed to a pre-determined temperature differentthan said first temperature.
 2. A cochlear implant electrode assemblydevice comprising: an elongate electrode carrier member made of aresiliently flexible first material and having a length and a pluralityof electrodes mounted thereon adapted to apply a preselected tissuestimulation, the elongate member having a pre-formed curved orientationthat at least substantially matches an inside surface of a cochlea, animplantable orientation different to said pre-formed orientation thatallows said member to be inserted into an implantee's cochlea, and an atleast one intermediate orientation between said implantable orientationand said pre-formed orientation; and a shape element removablypositioned within the elongate member and extending along at least aportion of the length thereof, said element having: a first shapeselected for biasing said elongate member into said implantableorientation when the shape element is at a first temperature; and atleast a second shape that allows the elongate member to adopt said atleast one intermediate orientation when the shape element is exposed toa temperature of the cochlea being different than said firsttemperature.
 3. A device of claim 1 wherein the pre-formed orientationof the elongate member is curved.
 4. A device of claim 3 wherein theelongate member adopts a spiral curvature when in the pre-formedorientation.
 5. A device of claim 1 or claim 2 wherein the shape elementis formed from a shape memory material that is relatively stiffer thanthe first material.
 6. A device of claim 5 wherein the shape memorymaterial is a metal or metal alloy, and the shape element biases theelongate member of the electrode array in at least a substantiallystraight orientation while the array is at a temperature different tohuman body temperature.
 7. A device of claim 5 wherein the shape memorymaterial is a plastics material.
 8. A device of claim 6 wherein theshape memory material is Nitinol™.
 9. A device of claim 6 wherein oninsertion into the body and exposure to body temperature, the shapeelement adopts at least the second shape.
 10. A device of claim 9wherein upon removal of the shape element the elongate member of theelectrode array adopts the implantable orientation.
 11. A device ofclaim 10 wherein upon removal of the shape element the elongateelectrode carrier member adopts its pre-formed curved orientation thatat least substantially matches an inside surface of a cochlea.
 12. Adevice of claim 2 wherein the elongate member is preformed from abiocompatible plastics material and has a first end that is firstlyinsertable into the implantee.
 13. A device of claim 12 wherein theelongate member is formed from a biocompatible material selected fromthe group comprising a silicone, and a polyurethane.
 14. A device ofclaim 12 wherein the shape element is removably positionable within alumen extending through the elongate member for at least a portion ofits length.
 15. A device of claim 14 wherein the lumen extends throughthe elongate member for a substantial portion of its length from anopening distal the first end to or adjacent the first end.
 16. A deviceof claim 15 wherein the shape element extends out of the openingallowing the element to be manipulated and removed from the lumen duringinsertion of the device.
 17. A device of claim 2 wherein the pluralityof electrodes are mounted along a surface of the elongated member thatat least substantially conforms to the inside surface of the cochlea.18. A device of claim 1 or claim 2 wherein the elongate member has anouter layer that acts as a stiffening sheath for the elongate member.19. A device of claim 18 wherein the stiffening sheath is formed of abioresorbable material which dissolves or softens on exposure to afluid.
 20. A device of claim 19 wherein the bioresorbable material ofthe stiffening sheath is selected from the group comprising polyacrylicacid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) andpolyglycolic acid (PGA).
 21. A device of claim 18 wherein the device hasan additional layer surrounding the stiffening sheath, the additionallayer having a first rate of fluid ingress therethrough and having atleast one fluid ingress means formed therein, the rate of fluid ingressthrough the fluid ingress means being greater than the first rate offluid ingress through the additional layer.
 22. A device of claim 21wherein the fluid ingress means comprise one or more openings in theadditional layer.
 23. A device of claim 1 or claim 2 wherein at least aportion of an outer surface of the elongate member can has a coating ofa lubricious material.
 24. A device of claim 23 wherein the lubriciousmaterial is selected from the group comprising polyacrylic acid (PAA),polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolic acid(PGA).
 25. A device of claim 12 wherein a resiliently flexible tipmember extends forwardly from the first end of the elongate member. 26.A device of claim 25 wherein the tip member has a plurality of metallicparticles dispersed therethrough.